The present invention relates generally to methods of fabricating electronics assemblies.
An electronics assembly may include one or more chips and a package carrier (such as a substrate, a circuit board, or a leadframe) to which each chip is attached. Electronics assemblies are found in virtually every electronic device constructed today. Each chip includes one or more integrated circuits fabricated using a wafer and an interconnect structure that facilitates connection of the devices with the external environment. The interconnect structure includes an array of electrically conductive contacts, known as bond pads, and intervening metals levels that couple the devices with the bond pads. Die cut from the wafer are mounted on the package carrier to form an electronics assembly.
Each die includes bond pads that are connected with bond pads on the package carrier to supply external electrical connections. In electronics assemblies formed by flip chip mounting, the bond pads on the die are electrically and physically connected by solder balls or bumps to a corresponding array of bond pads on a substrate, such as a package carrier. Typically, the solder bumps are registered with the bond pads on the die and/or substrate and reflow processes are applied to create physical and electrical connections in the form of solder joints. The process of flip chip mounting results in a gap between the die and the substrate that reflects the presence of the solder joints.
Frequently, an underfill is introduced into the gap between the die and the substrate and surrounding the solder bumps. The underfill is an electrically-insulating material that strengthens the mechanical bond between the die and substrate and protects the solder joints. The underfill is typically dispensed adjacent to one or more die edges and is drawn beneath the die by capillary action. However, the dispensed underfill has a tendency to migrate away from the dispensed location adjacent to the die and may contaminate an adjacent die. The resultant transport of underfill may lead to a premature failure of the electronics assembly. The probability of contamination of an adjacent die by underfill migration increases as the spacing between the adjacent die is reduced. Hence, underfill migration may be a limiting factor in establishing a minimum spacing between adjacent die in the electronics assembly.
In other types of electronics assemblies know as wire bond assemblies, the die is adhesively bonded to a die attach pad on a substrate. A wirebonding process is then used to couple wires between bond pads on the top surface of the die and bond pads distributed about the die attach pad. The bond pads are arranged about the outer circumference of the die attach pad. A die attach adhesive is dispensed onto the die attach pad. Because of their small size, the bond pads are highly sensitive to contamination by adhesive migrating from the die attach pad as a result of physically placing the die on the die attach pad.
Therefore, methods are needed for fabricating an electronics assembly that permit adjacent circuit elements to be positioned as close as physically possible without contamination of adjacent circuit elements from underfill or adhesive.